1. Field of the Invention
The present invention relates to a light irradiation heat treatment method and a light irradiation heat treatment apparatus in a manufacturing process of a semiconductor device.
2. Description of the Prior Art
In a semiconductor manufacturing process, a light irradiation heat treatment apparatus using a lamp is used for a short time-period heat treatment of, for example threshold voltage control of MOS transistor, impurity ion activation after ion implantation into sources, drains or the like, forming a silicide from a high melting point metal film, achieving low resistance of the metal silicide or the like. A typical configuration of this type of heat treatment apparatus is such that a plate-type workpiece is heated from either both sides or one side thereof using multiple lamps. The lamp is faced to a surface of the workpiece and the multiple lamps are arranged at a uniform density at a distance close to the surface. While the workpiece such as a semiconductor substrate is heat-treated at a substantially constant temperature, a feedback control is then performed to light irradiation intensity of the lamp so that the workpiece may be maintained at a predetermined temperature. In this case, the heat treatment apparatus measures a wavelength of an electromagnetic wave radiated from the heated workpiece, with a plurality of pyrometers disposed in the vicinity of either both sides or one side of the workpiece, and further converts it into a temperature. As described above, a process which feeds back the measured temperature by the pyrometer and controls the light irradiation intensity is called a closed circuit control process. This closed circuit control process works effectively at not less than a constant temperature at which sufficient radiation intensity is obtained from the workpiece. This temperature may typically be at 300° C. to 600° C. or more.
On the other hand, in an early phase of starting the heat treatment for the workpiece in the light irradiation heat treatment apparatus, there is a step of heating at a constant light irradiation intensity the workpiece at 300° C. to 600° C. or more which is a controllable temperature by the closed circuit control process, and this process is called an open loop control process. As described above, a light irradiation heat treatment comprises this open loop control process and the closed circuit control process.
Further, since the temperature rises as high as the temperature described above in a short time-period in a light irradiation heat treatment process, stress is applied to the workpiece, whereas consideration for relieving this is also made, and the art relative to that is described in, for example Japanese Patent Laid-Open Hei No. 11-214323 official report.
However, in the prior art described above, at the open loop control process immediately after starting the light irradiation in the light irradiation heat treatment apparatus, because of rapidly heating the workpiece at a constant light irradiation intensity, temperature rising speed usually changes in accordance with positions within the workpiece surface such as the semiconductor substrate or the like, resulting in a temperature distribution. The workpiece is therefore subjected to stress, so that there is caused distortion, deformation, warpage, crack or the like. Further, as a result of a crystal defect introduced to the workpiece in some cases, there has been a problem of causing a characteristic variation between semiconductor elements built in the semiconductor substrate to be the workpiece, and a defect in reliability or the like in addition to that.